<nz-dropdown>
  <a nz-dropdown>
    {{ ('language' | translate) || '语言' }} <i nz-icon type="down"></i>
  </a>
  <ul nz-menu nzSelectable>
    <li nz-menu-item (click)="changeLang('zh')">
      <a>中文</a>
    </li>
    <li nz-menu-item (click)="changeLang('en')">
      <a>English</a>
    </li>
  </ul>
</nz-dropdown>